Add support for exporting GCE disk images to GCS

[jleaniz]

This is a feature request to be used with dfTimewolf and OpenRelik.

We would like to be able to export images as described here. This will be used with OpenRelik's GCS file importer.

[Fryyyyy]

Do we not already have this ?

  def ExportImage(
      self, gcs_output_folder: str, output_name: Optional[str] = None) -> None:
    """Export compute image to Google Cloud storage.

    Exported image is compressed and stored in .tar.gz format.

    Args:
      gcs_output_folder (str): Folder path of the exported image.
      output_name (str): Optional. Name of the output file. Name will be
          appended with .tar.gz. Default is [image_name].tar.gz.

    Raises:
      InvalidNameError: If exported image name is invalid.
    """

[jleaniz]

Possibly? I saw that the gcloud command lets you specify the export format, maybe it's just another argument we need to pass to the API call. I believe @berggren had been using qcow2. @berggren can you confirm this is sufficient for what we need for exporting images?

[Fryyyyy]

Output is raw disk (just dd) then tar'red and gz'ed

[Fryyyyy]

But it can support others:
Valid formats include vmdk, vhdx, vpc, vdi, and qcow2.

Could add this as a parameter